Cards are a common organizing unit for modern user interfaces (UI). At their core, they’re just rectangular containers with borders and padding. However, when utilized properly to group related information, they help users better digest, engage, and navigate through content. This is why most successful dashboard/UI frameworks make cards a core feature of their component library. This article provides an overview of the API that bslib provides to create Bootstrap cards.
Setup code
To demonstrate that bslib cards work outside of Shiny (i.e., in R Markdown, static HTML, etc), we’ll make repeated use of statically rendered htmlwidgets like plotly and leaflet. Here’s some code to create those widgets:
library(bslib)
library(shiny)
library(htmltools)
library(plotly)
library(leaflet)
plotly_widget <- plot_ly(x = diamonds$cut) %>%
config(displayModeBar = FALSE) %>%
layout(margin = list(t = 0, b = 0, l = 0, r = 0))
leaflet_widget <- leafletOptions(attributionControl = FALSE) %>%
leaflet(options = .) %>%
addTiles()Shiny usage
Cards work equally well in Shiny. In the
examples below, replace plotly_widget with
plotlyOutput() and leaflet_widget with
leafletOutput() to adapt them for Shiny server-rendered
plots/maps.
Hello card()
A card() is designed to handle any number of “known”
card items (e.g., card_header(), card_body(),
etc) as unnamed arguments (i.e., children). As we’ll see shortly,
card() also has some useful named arguments (e.g.,
full_screen, height, etc).
At their core, card() and card items are just an HTML
div() with a special Bootstrap class, so you can use
Bootstrap’s utility classes to customize things like colors,
text, borders,
etc.
card(
card_header(
class = "bg-dark",
"A header"
),
card_body(
markdown("Some text with a [link](https://github.com)")
)
)Some text with a link
Implicit card_body()
If you find yourself using card_body() without changing
any of its defaults, consider dropping it altogether since any direct
children of card() that aren’t “known” card()
items, are wrapped together into an implicit card_body()
call.1
For example, the code to the right generates HTML that is identical to
the previous example:
card(
card_header(
class = "bg-dark",
"A header"
),
markdown("Some text with a [link](https://github.com).")
)Some text with a link.
Restricting growth
By default, a card()’s size grows to accommodate the
size of its contents. Thus, if a card_body() contains a
large amount of text, tables, etc., you may want to specify a
height or max_height. That said, when laying
out multiple cards, it’s likely best not
to specify height on the card(), and instead, let the
layout determine the height layout_column_wrap().
Although scrolling is convenient for reducing the amount of space
required to park lots of content, it can also be a nuisance to the user.
To help reduce the need for scrolling, consider pairing scrolling with
full_screen = TRUE (which adds an icon to expand the card’s
size to the browser window). Notice how, when the card is expanded to
full-screen, max_height/height won’t effect
the full-screen size of the card.
card(
max_height = 250,
full_screen = TRUE,
card_header(
"A long, scrolling, description"
),
lorem::ipsum(paragraphs = 3, sentences = 5)
)Ipsum nam per magnis malesuada et cum auctor natoque sagittis varius lacus tellus ridiculus. Sem leo nisl; posuere magna nascetur – iaculis sociosqu facilisis a tortor facilisi dictum. Vulputate habitant nisi id. Commodo convallis platea aptent at dictum nostra – parturient, et faucibus. Mattis scelerisque ad taciti at ligula velit fames.
Elit pellentesque orci vulputate non ligula; cubilia suspendisse a nisl vehicula? Erat senectus magnis – sollicitudin aliquet malesuada magnis id libero facilisi purus. Platea nostra posuere massa cursus tortor volutpat massa, nisl ante dapibus. Rutrum felis nulla praesent varius accumsan libero quis ut justo hac? Bibendum sociis est.
Adipiscing curae class, suspendisse ultrices dis malesuada eu molestie. Et eros proin – commodo fermentum dignissim mauris. Ullamcorper facilisis pretium massa netus sociis inceptos velit feugiat? Fermentum vestibulum iaculis mauris nostra euismod consequat porta nisl non suscipit? Lobortis vulputate velit – ornare est neque integer facilisi elementum sociosqu felis.
Filling outputs
A card()’s default behavior is optimized for
facilitating filling layouts. More
specifically, if a fill item (e.g.,
plotly_widget), appears as a direct child of a
card_body(), it resizes to fit the card()s
specified height. This means, by specifying height = 250
we’ve effectively shrunk the plot’s height from its default of 400 down
to about 200 pixels. And, when expanded to full_screen, the
plot grows to match the card()’s new size.
card(
height = 250,
full_screen = TRUE,
card_header("A filling plot"),
card_body(plotly_widget)
)Most htmlwidgets (e.g., plotly, leaflet, etc) and some other Shiny
output bindings (e.g, plotOutput(),
imageOutput(), etc) are fill items by
default, so this behavior “just works” in those scenarios. And, in some
of these situations, it’s helpful to remove card_body()’s
padding, which can be done via spacing
& alignment utility classes.
card(
height = 275,
full_screen = TRUE,
card_header("A filling map"),
card_body(
class = "p-0",
leaflet_widget
),
card_footer(
class = "fs-6",
"Copyright 2023 RStudio, PBC"
)
)Fill item(s) aren’t limited in how much they grow
and shrink, which can be problematic when a card becomes very small. To
work around this, consider adding a min_height on the
card_body() container. For example, try using the handle on
the lower-right portion of this card example to make the card
taller/smaller.
This interactive example is a bit contrived in that we’re using CSS
resize to demonstrate how to make plots that don’t shrink beyond a
certain point, but this concept becomes quite useful when implementing
page-level filling layouts (i.e.,
page_fillable()) with multiple
cards.
card(
height = 300,
style = "resize:vertical;",
card_header("Plots that grow but don't shrink"),
card_body(
min_height = 250,
plotly_widget,
plotly_widget
)
)Troubleshooting fill
As you’ll learn more about in filling
layouts, a fill item loses its ability to fill when
wrapped in additional UI element that isn’t a fillable
container. To fix the situation, use as_fill_carrier() to
allow the additional element to carry the potential to fill from the
card_body() down to the fill item.
Multiple card_body()
A card() can have multiple card_body()s,
which is especially useful for:
- Combining both resizable and non-resizable contents (i.e., fill items and non-fill).
- Allowing each
card_body()to have their own styling (via inline styles and/or utility classes) and resizing limits (e.g.,min_height).
For example, when pairing filling output with scrolling content, you
may want min_height on the filling output since the
scrolling content will force it to shrink:
card(
height = 375,
full_screen = TRUE,
card_header(
"Filling plot, scrolling description"
),
card_body(
min_height = 200,
plotly_widget
),
card_body(
class = "lead container",
lorem::ipsum(paragraphs = 10, sentences = 5)
)
)Consectetur natoque augue molestie platea parturient purus tempus vitae? Eros fames laoreet aenean, pharetra condimentum, lacus torquent eleifend commodo placerat dui pharetra. Sed blandit varius erat blandit aptent class velit, eros convallis sollicitudin nam platea lectus? Justo turpis condimentum laoreet tempus condimentum tortor: fermentum nulla nunc, aptent eu at lectus? In integer auctor cum blandit augue nulla, integer tristique sollicitudin.
Dolor lobortis cubilia ultrices laoreet. Curabitur placerat auctor netus, integer sodales feugiat vulputate lacinia id proin? Scelerisque congue quis porta tortor curae cursus. Commodo arcu tellus lacinia, cum massa ullamcorper. Interdum fames iaculis torquent nunc hac parturient lacinia porttitor, ac, suscipit justo; mattis primis tristique placerat velit habitasse suspendisse at eget suscipit tincidunt dui eleifend.
Ipsum sociosqu natoque ante ultrices fringilla, non lobortis donec venenatis! Praesent eu praesent maecenas ac conubia phasellus, fermentum quam ligula. Magna dapibus bibendum turpis risus urna, rhoncus cursus elementum auctor! A hac arcu ante a euismod mauris odio, taciti in? Sed conubia diam congue sapien sollicitudin scelerisque cubilia lacus!
Sit est etiam nostra molestie vulputate odio, sagittis euismod elementum felis. Pretium odio habitasse conubia accumsan nulla dictumst. Tincidunt suscipit blandit montes litora metus lectus vulputate nascetur mollis etiam. Risus duis netus magna, praesent dapibus egestas suspendisse dictum cras ornare nisl. Parturient nunc cursus erat, consequat primis porttitor habitasse turpis.
Dolor senectus metus ut volutpat dis interdum lectus fusce ligula et rutrum. Fames aptent suscipit dictum taciti fermentum, habitasse sociis habitasse sociosqu elementum. Aptent imperdiet enim hac sapien malesuada, laoreet, taciti nibh per nunc. Habitant rhoncus neque, praesent bibendum ac primis massa vehicula posuere vitae? Primis posuere class euismod nam non vivamus inceptos dui; lobortis cras sociosqu?
Sit pellentesque hac tristique viverra porttitor: in quam gravida sem nostra dis primis. Duis egestas, eget fames leo consequat parturient suspendisse ornare, malesuada ad odio commodo? Massa suspendisse parturient pharetra mollis cras tempus nostra felis: tincidunt cum posuere? Molestie scelerisque urna nascetur – odio sociosqu bibendum facilisi non et cursus inceptos ad? Na ad.
Elit risus posuere dictumst iaculis cursus habitant pellentesque penatibus. Pharetra netus vel elementum nisl dignissim cursus; tempor iaculis facilisi laoreet class neque. Bibendum cum at iaculis fames phasellus suspendisse magnis. Duis non sapien; morbi blandit phasellus penatibus libero auctor. Fames magnis suspendisse arcu fringilla, nostra nisi elementum netus nisi accumsan viverra nam aptent justo nostra ac.
Lorem hendrerit ut porttitor hac sed, in montes curae netus libero in. Velit justo elementum commodo metus leo lectus fermentum, mus scelerisque tincidunt? Fusce conubia dapibus, torquent himenaeos facilisi venenatis varius, nec netus potenti. Mi platea nisi vitae faucibus curabitur rutrum eleifend. Leo in enim vestibulum venenatis ut volutpat etiam!
Amet vitae donec tellus fringilla volutpat. Dapibus ornare venenatis libero ultrices potenti torquent: molestie enim torquent. A interdum tortor lacinia libero vestibulum. Neque netus conubia vehicula ullamcorper curae, sodales inceptos nulla viverra lacinia volutpat. Proin nec condimentum litora!
Ipsum class sociis et in odio aliquam. Maecenas dis: diam torquent rhoncus quisque gravida rutrum maecenas vulputate luctus inceptos. Feugiat aliquet suscipit velit velit et aliquam vehicula duis sodales posuere lectus! Nisi varius: ad nunc lacus lobortis cras ac purus. Sagittis molestie rutrum fermentum consequat metus.
Also, when the content has a fixed size, and should not be allowed to
scroll, set fill = FALSE:
card(
height = 350,
full_screen = TRUE,
card_header(
"Filling plot, short description"
),
plotly_widget,
card_body(
fill = FALSE, gap = 0,
card_title("A subtitle"),
p(class = "text-muted", "And a caption")
)
)A subtitle
And a caption
Multiple columns
As you’ll learn in column-based
layouts, layout_column_wrap() is great for multi-column
layouts that are responsive and accommodate for filling output. Here we have an equal-width
2-column layout using width = 1/2, but it’s also possible
to have varying column
widths.
card(
height = 350,
full_screen = TRUE,
card_header("A multi-column filling layout"),
card_body(
min_height = 200,
layout_column_wrap(
width = 1/2,
plotOutput("p1"),
plotOutput("p2")
)
),
lorem::ipsum(paragraphs = 3, sentences = 5)
)Adipiscing dui mus, dignissim integer penatibus curae feugiat ultrices laoreet pellentesque. Dignissim molestie congue curabitur aliquet nostra, a lacus accumsan sodales gravida suscipit. Imperdiet dis maecenas rhoncus tincidunt dictumst pharetra tempor bibendum nullam velit pharetra. Blandit magna suspendisse at vel: cubilia quam auctor cum ultricies? Ridiculus.
Dolor auctor lacinia vehicula mollis scelerisque mattis vulputate sociis lectus. Nisl rhoncus curae pellentesque mollis molestie massa, habitant ultricies! Eget felis cubilia, sollicitudin non lacinia, habitant mattis tempus vel. Integer lacus at lobortis mollis aliquam dictumst – dictumst, sem enim. Enim habitant quis senectus, fermentum mi; inceptos nisi lectus rhoncus auctor vestibulum tristique litora.
Adipiscing blandit habitasse consequat sodales convallis quisque. Et nulla ullamcorper metus imperdiet tempus habitant aptent; litora semper. Nunc justo eu quisque a luctus lacinia a mi augue! Platea sed mus, fermentum, felis sodales, conubia lacus congue praesent. Augue purus lobortis potenti euismod.
Multiple cards
layout_column_wrap() is especially nice for laying out
multiple cards since each card in a particular row will have the same
height (by default). Learn more in column-based layouts.
layout_column_wrap(
width = 1/2,
height = 300,
card(full_screen = TRUE, card_header("A filling plot"), plotly_widget),
card(full_screen = TRUE, card_header("A filling map"), card_body(class = "p-0", leaflet_widget))
)Multiple tabs
navset_card_tab() and navset_card_pill()
make it possible to create cards with multiple tabs or pills. These
functions have the same full_screen capabilities as normal
card()s as well some other options like title
(since there is no natural place for a card_header() to be
used). Note that, each nav_panel() object is similar to a
card(). That is, if the direct children aren’t already card
items (e.g., card_title()), they get implicitly wrapped in a
card_body().
library(leaflet)
navset_card_tab(
height = 450,
full_screen = TRUE,
title = "HTML Widgets",
nav_panel(
"Plotly",
card_title("A plotly plot"),
plotly_widget
),
nav_panel(
"Leaflet",
card_title("A leaflet plot"),
leaflet_widget
),
nav_panel(
shiny::icon("circle-info"),
markdown("Learn more about [htmlwidgets](http://www.htmlwidgets.org/)")
)
)Sidebars
As you’ll learn more about in sidebar
layouts, layout_sidebar() just works when placed inside
in a card(). In this case, if you want fill
items (e.g., plotly_widget) to still fill the card
like we’ve seen before, you’ll need to
set fillable = TRUE in layout_sidebar().
card(
height = 300,
full_screen = TRUE,
card_header("A sidebar layout inside a card"),
layout_sidebar(
fillable = TRUE,
sidebar = sidebar(
actionButton("btn", "A button")
),
plotly_widget
)
)Static images
card_image() makes it easy to embed static (i.e.,
pre-generated) images into a card. Provide a URL to href to
make it clickable. In the case of multiple card_image()s,
consider laying them out in multiple cards
with layout_column_wrap() to produce a grid of clickable
thumbnails.
card(
height = 300,
full_screen = TRUE,
card_image(
file = "shiny-hex.svg",
href = "https://github.com/rstudio/shiny"
),
card_body(
fill = FALSE,
card_title("Shiny for R"),
p(
class = "fw-light text-muted",
"Brought to you by RStudio."
)
)
)
Shiny for R
Brought to you by RStudio.
Flexbox
Both card() and card_body() default to
fillable = TRUE (that is, they are CSS flexbox
containers), which works wonders for facilitating filling outputs, but it also leads to
surprising behavior with inline tags (e.g., actionButton(),
span(), strings, etc). Specifically, each inline tag is
placed on a new line, but in a “normal” layout flow
(fillable = FALSE), inline tags render inline.
card(
card_body(
fillable = TRUE,
"Here's some", tags$i("inline"), "text",
actionButton("btn1", "A button")
),
card_body(
fillable = FALSE,
"Here's some", tags$i("inline"), "text",
actionButton("btn2", "A button")
)
)That said, sometimes working in a flexbox layout is quite useful,
even when working with inline tags. Here we leverage flexbox’s gap
property to control the spacing between a plot, a (full-width) button,
and paragraph. Note that, by using markdown() for the
paragraph, it wraps the results in a <p> tag, which
means the contents of the paragraph are not longer subject to
flexbox layout. If we wanted, we could do something similar to render
the actionButton() inline by wrapping it in a
div().
card(
height = 325, full_screen = TRUE,
card_header("A plot with an action links"),
card_body(
class = "gap-2 container",
plotly_widget,
actionButton(
"go_btn", "Action button",
class = "btn-primary rounded-0"
),
markdown("Here's a _simple_ [hyperlink](https://www.google.com/).")
)
)In addition to gap, flexbox has really nice ways of handling otherwise difficult spacing and alignment issues. And, thanks to Bootstrap’s flex utility classes, we can easily opt-in and customize defaults.
card(
height = 300, full_screen = TRUE,
card_header(
class = "d-flex justify-content-between",
"Centered plot",
checkboxInput("check", " Check me", TRUE)
),
card_body(
class = "align-items-center",
plotOutput("id", width = "75%")
)
)Shiny
Since this article is statically rendered, the examples here use
statically rendered content/widgets, but the same card()
functionality works for dynamically rendered content via Shiny (e.g.,
plotOutput(), plotlyOutput(), etc).
An additional benefit that comes with using shiny is the ability to
use getCurrentOutputInfo() to render new/different content
when the output container becomes large enough, which is particularly
useful with card(full_screen = T, ...). For example, you
may want additional captions/labels when a plot is large, additional
controls on a table, etc (see the value
boxes article for a clever use of this).
# UI logic
ui <- page_fluid(
card(
max_height = 200,
full_screen = TRUE,
card_header("A dynamically rendered plot"),
plotOutput("plot_id")
)
)
# Server logic
server <- function(input, output, session) {
output$plot_id <- renderPlot({
info <- getCurrentOutputInfo()
if (info$height() > 600) {
# code for "large" plot
} else {
# code for "small" plot
}
})
}
shinyApp(ui, server)Appendix
The following CSS is used to give plotOutput() a
background color; it’s necessary here because this documentation page is
not actually hooked up to a Shiny app, so we can’t show a real plot.